Kindle for iPhone is the official application of Amazon thanks to which you can read eBooks on your iDevice for the Kindle reader.
With Kindle for iPhone you are no longer physically forced to have an eReader to read one of the many ebooks for sale on Amazon.
Also you can buy, download and read them comfortably on iPhone, iPad or iPod touch.Kindle for iPhone syncs with your Amazon account.
With Kindle for iOS, optimized for iPhone, iPod touch and iPad, you can have mobile access to over 1,000,000 books in the Kindle Store.
The App offers an interesting feature called Amazon Whispersync, which automatically synchronizes the last page read, bookmarks and notes, highlighting it all devices, including Kindle, so you can continue reading on other devices in the last page where you stopped.
This way you can find them ready as you are reading the same book on a Kindle device or on the client PC.